When inserting a new device in a network, particularly when the new device is inserted between a pair of devices that would otherwise be directly connected together over Ethernet, there is a risk that the new device may impact the results of a negotiation of the Ethernet settings between the original pair of devices.
For instance, a disparity in the negotiation of the settings could occur when only one device is up when the intermediate device is started. This could result in the negotiation of a half-duplex Ethernet connection on one port of the intermediate device while the other port of the intermediate device negotiates a full-duplex Ethernet connection with the other remote device.
Another problem to handle is when there is only a single device connected to the intermediate device at a given time. Under such a scenario, the device connected to the intermediate device shall be able to operate at the highest possible speed supported by that said device and not have to wait for a second device to be connected to the intermediate device before it can negotiate the settings of the Ethernet connection.
In a typical 1000BaseT Ethernet protocol stack, the Physical Coding Sub-layer (PCS —see FIG. 3 “37-1-Location of the Auto-Negotiation function” from the IEEE 802.3-2008 standard) is responsible for the negotiation of the Ethernet settings for a specific Ethernet port on a device. The harmonization of the negotiation of the Ethernet settings for multiple ports in a single device is not covered by the IEEE 802.3-2008 standard.
There is a need to allow the ability to inspect and operate on Ethernet frames received over any of the ports of an intermediate device once the auto-negotiation phase is completed.